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Assessing Binocular Central Visual Field and Binocular Eye Movements in a Dichoptic Viewing Condition
Published on: July 21, 2020
The spoke brightness illusion originates at an early motion processing stage.
A O Holcombe1, J Intriligator, P U Tse
1Department of Psychology, Harvard University, 33 Kirkland St., Cambridge, MA 02138, USA. holcombe@wjh.harvard.edu
Perception & Psychophysics
|January 5, 2001
Summary
The spoke illusion, where a dark gray line appears to connect a rotating disk to a central point, is caused by retinal motion. This visual illusion is strongest with high luminance contrast and diminishes as contrast decreases.
Area of Science:
- Visual perception
- Motion processing
- Illusory phenomena
Background:
- The spoke illusion is a visual phenomenon where a dark gray region appears to connect a revolving white disk to a central fixation point against a gray background.
- Previous understanding of visual illusions often involves complex processing, but the underlying mechanisms for the spoke illusion were not fully elucidated.
Purpose of the Study:
- To investigate the necessary and sufficient conditions for the perception of the spoke illusion.
- To determine the role of retinal motion and luminance contrast in the spoke illusion.
- To ascertain the stage of visual processing at which the spoke illusion originates.
Main Methods:
- Experiment 1: Manipulated perceived motion versus actual retinal motion of a revolving disk to assess necessity and sufficiency.
- Experiment 2: Varied luminance contrast of the disk against the background, including subjective equiluminance, to measure illusion strength.
- Utilized psychophysical methods to quantify the perception of the spoke illusion under controlled visual conditions.
Main Results:
- Retinal motion, irrespective of perceived stationarity, was found to be both necessary and sufficient for the spoke illusion.
- The strength of the spoke illusion decreased with decreasing luminance contrast, becoming negligible at subjective equiluminance.
- The illusion persisted even when the visual system might be expected to discount motion (e.g., during smooth pursuit).
Conclusions:
- The spoke illusion arises from an early stage of visual processing that is primarily driven by luminance.
- This early motion processing occurs before the visual system compensates for retinal motion generated by smooth pursuit eye movements.
- The findings highlight the fundamental role of luminance-based retinal motion detection in generating specific visual illusions.
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